Various compressed air foam systems (CAFS) have been used in firefighting applications. In its most basic form, a CAFS is simply a means for mixing air and water with a surfactant in order to produce a water-based foam that is used to extinguish fires. CAFS provides quicker “knockdown” against potent fires, deeper penetration of fuels, and gives firefighters the advantage of making their initial attack against a fire from a significantly greater distance than with a traditional water stream or fog pattern. The bubble structure allows for greater expansion of delivered water surface area, allowing for greater heat reduction compared to equal amounts of plain water. Foam blankets allow for pre-treatment of fuels that are not already involved in the fire, and have less adverse impact on property, as well as helping to prevent damage to evidence used for fire investigations. In fact, some studies have indicated that CAFS increases the effectiveness of water as an extinguishing agent by approximately a factor of five. CAFS may be particularly valuable for rural fire departments, because the use of foam reduces the amount of water required to extinguish a fire, and rural departments are often quite limited in the amount of water that they have available at any particular fire.
One problem raised by the adoption of OAFS systems is that there may be certain applications where, even though a OAFS system is available, it is desirable to use only water in fighting a particular fire. For example, this may be desired if solution is not immediately available. It would be advantageous if the OAFS system could simply be deactivated in the field without the removal of any equipment, thereby allowing simple water flow. Likewise, it would be advantageous if the OAFS system allowed for the relatively unrestricted flow of solution rather than water, where “solution” is a combination of water and surfactant without the injection of air to produce foam. Solution has been shown to be more effective than simple water in suppressing certain types of fires, and there are firefighting applications where it is deemed more desirable than OAFS. Another advantage would be to allow for the combination of either water or solution flow with OAFS production to produce a “wet OAFS” flow, thereby giving the firefighter a full selection of operating modes that may be utilized in order to best address a particular firefighting scenario arising in the field. It would also be desirable to develop such a system without the need for complex bypass piping, in order to keep the cost of any new apparatus or necessary retrofit on an existing apparatus as low as possible and minimize the on-board space required for the retrofit.
In addition, it would be desirable to develop a OAFS system that could be used to deliver water-only flow at a maximum rate when the OAFS equipment is deactivated, just as if the system would deliver if no OAFS equipment were present, that is, as if the water were simply passing through straight pipe rather than through the OAFS equipment. This would allow for the greatest possible flow rate of water when a large amount of water is available and is desired for effectively suppressing a particular fire.
Finally, it would be desirable to develop a OAFS system that provides the highest possible water/solution flow rate during foam production for a given size of inlet line. In those applications where the amount of water/solution available is not a limiting factor, firefighting capacity can be increased by increasing the quantity of foam that may be delivered to a particular application. Some existing OAFS systems use various devices and features for mixing of the solution and air, which tend to impede the flow of foam to the application. It would be desirable to develop a system that provides a minimum of flow resistance, thereby maximizing foam delivery rates, while still providing a high quality foam through adequate mixing of the solution water and air within the OAFS mixing chamber.
Devices or references mentioned in this background section are not admitted to be prior art with respect to the present invention.